WO1993004010A1 - Furnace with thermal insulation, and method of manufacture - Google Patents

Abstract

The invention concerns a furnace (1) with an inner wall (2), an outer wall (3) and, located between them, thermal insulation (4). The thermal insulation is foamed and cured in situ, from a preparation containing: for every 100 parts by wt. of a reactive solid (block-forming component), 40-250 parts by wt. of a water-containing hardner which initiates the curing reaction of the reactive solid (block-forming component) in the alkaline pH-range, 40-250 parts by wt. of fillers, plus a foaming agent. The reactive solid is preferably one of the following: I) a finely divided oxide mixture containing amorphous silicon dioxide and aluminium oxide; II) glassy amorphous electrostatic-filter ash; III) ground calcined bauxite; IV) electrostatic-filter ash from lignite-fired power stations; V) undissolved amorphous SiO2; particularly that obtained from amorphous anhydrous or hydrated silicic acid in disperse powder form or from high-temperature processes (silica fumes); VI) metakaolin.

Description

 Insulated furnace and process for its manufacture

Technical field

The invention relates to a furnace with an inner wall, an outer wall and a thermal insulation arranged between the inner wall and the outer wall, a method for producing a furnace and the use of an inorganic foam which foams and cures from an inorganic curable composition is used for the insulation of furnaces and as a front material in melting, holding and dosing furnaces and for lining and coating furnace accessories.

The invention relates in particular to furnaces for molten metals such as warro holding, dosing and melting furnaces, in particular in the non-ferrous (NE) range.

Metal melting furnaces and other furnaces both in the liquid metal area and in the heating and burner area require highly effective and temperature-resistant insulation. This is necessary both for reasons of process technology and for reasons of energy saving.

State of the art

In a conventional method for producing furnaces for molten metals, such as holding, dosing and melting furnaces, an outer trough made of steel is first produced, which is internally covered with a plurality of overlapping layers of insulating plates or mats made of e.g. B. ceramic fibers is lined.

After inserting the insulation, an inner casing is used to form a space. A fire-resistant concrete is then poured into this intermediate space between the fiberboard insulation and the inner formwork, which after hardening represents the inner wall of the furnace.

This application of e.g. B. Insulating fibreboard is extremely labor intensive since the fiberboard must be cut, fitted and attached by hand due to the relatively complicated geometry of the furnaces. On this iso- In practice, it is not uncommon for more than 50% of the total manufacturing costs of such a furnace to fall.

In addition, there are always undesired gaps and gaps, which on the one hand adversely affects the strength of the insulating layer and on the other hand creates thermal bridges which, in addition to energy losses, also lead to damage to the furnace structure and to accidents if liquid metal escapes can.

Another disadvantage of the known furnaces is that liquid metal can get into the insulating layer in the event of a crack or other damage to the inner wall, this often being completely penetrated by the molten metal and thus becoming unusable. A repair is only possible by completely replacing the entire insulation and the inner wall.

Casting from insulating concrete or other materials is also known. These solutions are very complex to process and very expensive in terms of material. Health damage can also occur during processing.

OBJECT The object of the invention is to create a furnace with thermal insulation arranged between an inner and an outer wall, in which the thermal insulation is simple and inexpensive to produce, has high strength and avoids the formation of thermal bridges.

Another object of the invention is to provide a furnace for liquid metals with a heat insulation that is resistant and penetration-proof to liquid metal melts.

Finally, it is a further concern of the invention to provide a material for the thermal insulation of metal furnaces which, in addition to the insulation of the furnace pan, is also used for insulating Is suitable for furnace accessories such as hoods, covers, lids, channels, chimneys, etc.

DESCRIPTION OF THE INVENTION This object is achieved according to the invention by the characterizing features of claims 1 and 11 and by the features of claims 13, 14 and 15.

It is an essential feature of the invention that the thermal insulation is foamed and cured in situ, ie directly at the point to be insulated in the furnace. According to a preferred method of manufacturing a furnace, the outer wall, e.g. B. in a known manner made of steel, and the inner wall made separately. The inner wall can be created in a manner known to the person skilled in the art by casting, ramming or spraying from refractory concrete or other refractory masses or by walls made from refractory bricks. In principle, the inner tub can also be produced in other ways known to the person skilled in the art, e.g. B. made of ceramic plates that are screwed together and sealed against each other. The fully hardened and preferably annealed inner wall is then placed in the outer wall in such a way that a distance remains between the outer and the inner wall which corresponds to the desired thickness of the insulation. A mixture of reactive solid, water-containing alkaline hardener, fillers and blowing agent is then poured into this intermediate space, only about 10 to 30 percent by volume being required, depending on the foaming factor set (amount of blowing agent). Possibly. the oven can be warmed up slightly (ax. approx. 50 to 80 ° C) to accelerate the hardening. However, it is usually possible to work at room temperature, as the foaming agent decomposes (preferably H ₂ O ₂ ) and through the exothermic reaction of the mass is released enough heat to heat the foamed mass to about 60 to 90 ° C. and harden within 0.5 to 5 hours.

The use of an inorganic foam for thermal insulation, which is foamed and cured in situ from an inorganic curable composition, results in a hanging, continuous and therefore relatively solid insulating layer, which prevents the formation of thermal bridges. Filling the inorganic curable composition into the cavities or applying it to the surfaces to be insulated requires little effort. The inorganic foamable and curable compositions used according to the invention are known in principle; B. DE-C2 35 12 515, WO 89/05783, EP-A2 0 199 941, EP-Bl 0 148 280, but their suitability for in-situ insulation of furnaces was not to be expected.

It has surprisingly been found that the foamable and curable composition used according to the invention is absolutely resistant and tight to molten metal in the cured state. This means that even if the inner wall of the furnace leaks, the insulation effect is not impaired.

The foam has a good insulating effect, is light, inexpensive and, when fully reacted, is not harmful to health. Outbreak does not have to be stored in hazardous waste landfills. The foam is resistant to many substances and, depending on the composition, has a temperature resistance of up to 1200 ° C.

Preferred formulations for the foamable composition are given in claims 4 to 6. They are available as commercial products under the name TROLIT ^R hardener or TROLIT ^R solid material from Hüls Troisdorf AG.

The mass required for the production of a furnace, in which the insulation is arranged between an inner wall and an outer wall, which is expanded and cured with increasing volume to form an incombustible foam, is prepared by mixing the components either by hand or by machine. The mass contains 40 to 250 parts by weight of a water-containing hardener per 100 parts by weight of a reactive solid (stone-forming component), which causes the hardening reaction of the reactive solid in the alkaline range, 40 to 250 parts by weight of fillers and a Propellant. The mass is filled into the cavities of the furnace to be insulated or between the inner wall and the outer wall, and foams due to the chemical reaction which begins with a considerable increase in volume, as a result of which the cavities are completely filled. It is impossible for gaps and gaps to remain. The mass then hardens in an exothermic reaction.

In the manufacture of furnaces, mineral or ceramic fiber plates or mats are preferably applied to the inner wall in at least a partial area of their surface before the remaining intermediate or hollow space is then foamed. The fiberboard or mat has a higher elongation at break than the cured foam, which increases the resistance to temperature changes and reduces the tendency to crack when subjected to temperature changes. The cured inorganic foam is at least largely closed-cell.

The inorganic foam preferably forms - with the exception of

Breakthroughs in the walls - a completely closed area between the inner wall and the outer wall of the furnace.

The furnaces with such thermal insulation can be produced for a wide variety of applications, in particular for melting, holding and dosing furnaces.

The reactive solids (stone-forming components) contained in the inorganic curable composition preferably contain one or more reactive solids from the group

I a finely divided oxide mixture with contents of amorphous silicon dioxide and aluminum oxide, in particular as electrostatic filter dust from the manufacture of aluminum oxide,

II a glassy, amorphous electrostatic filter ash, III a ground calcined bauxite,

IV an electrostatic precipitator ash from lignite-fired power plants,

V of an undissolved, amorphous silicon dioxide (SiO 2), in particular from an amorphous, disperse powdery, ent aqueous or water-containing silica or from high temperature processes (silica fume), VI of a metakaolin.

The water-containing hardener present in the inorganic curable composition to form the inorganic foam is preferably an alkali silicate solution with 1.2 to 2.5 mol SiO 2 each

In particular, mica and fine-grained talc are used as fillers in the foamable and curable inorganic mass.

After the foam has been foamed and hardened from the curable inorganic composition, it has a density of 120 to 350 kg / m 2, the desired density being able to be set within relatively wide limits via the amount of blowing agent.

The thermal insulation consisting of the inorganic foam is not only suitable for use in ovens, but also for their accessories. The furnace systems in question are, for example, furnace systems for foundries for metal treatment of solid and liquid metals, in particular Al, Zn, GG, GS melting, holding and dosing furnaces for molten metals, the inorganic foam being impermeable and resistant is against the molten metal, or furnace systems for recycling processes such as chip drying, sand regeneration, burn-out furnaces (epoxilite) and for thermal post-combustion.

The accessories for these furnace systems, which are lined or coated with the inorganic foam, are, for. B. hoods, covers, lids, channels, doors and chimneys as well as transport pans for liquid metal and preheating systems.

The foam not only serves as insulation against heat loss, but also as sound insulation. Brief description of the drawing

The invention is explained in more detail below on the basis of an exemplary embodiment and the drawing. 1 shows a furnace for metal melts produced according to the invention in vertical section,

2 shows a furnace for metal melting produced according to the invention in horizontal section, FIG. 3 shows the detail X according to FIG. 1,

Fig. 4 detail X of FIG. 1 according to an alternative embodiment of the invention.

Best way to carry out the invention

To produce an aluminum holding furnace 1 with a capacity of 750 kg of molten metal 6, the outer wall 3 is first made of 5 mm thick steel sheet.

In parallel, the inner wall 2 is poured from refractory concrete with a wall thickness of 100 mm and annealed at 700 ° C for 5 to 7 days. This intrinsically stable trough is then completely pre-insulated on the side surfaces 8 with 30 mm thick insulating plates 5 made of ceramic fibers (detail X, FIG. 3).

In the outer trough made of sheet steel (outer wall 3), some floor supports 7 with a height of 220 mm are placed, on which the inner trough is then placed, a distance of 220 mm remaining between the inner wall 2 and the outer wall 3.

The following approach is used for the foamable and curable mass:

a) Reactive solid: TROLIT ^R reaction type ROS

(Filter dust from an electrostatic precipitator cleaning one

Electric melting furnace for the production of electric corundum; contains a fine-particle oxide mixture with contents of amorphous silicon dioxide and aluminum oxide). b) filler: 65.5% by weight of fine-grained talc

33% by weight of magnesium mica (PHLOGOPIT) 1.5% by weight of alkali-resistant glass fibers.

c) Hardener: TROLIT ^R hardener type AOS (51.4% by weight water,

25.5% by weight of SiO ₂ dissolved, 23.1% by weight of K ₂ Oj. d) Foaming agent: 10% by weight H2O2

The total batch consists of 22% by weight reactive solid, 34% by weight filler, 36% by weight hardener, 8% by weight foaming agent.

First, solid, filler and hardener are mixed homogeneously with each other in an alkali-resistant mixer. The propellant is metered in only immediately before the somewhat viscous mass is introduced into the space between the inner wall 2 and the outer wall 3. Either the foaming agent is continuously mixed into the intermediate space when the mass is filled (combined feed and metering pump), or the mass is mixed in portions with blowing agent and poured in immediately. The required amount of the foamable mass is approximately 1/4 to 1/5 of the volume of the space to be filled, depending on the desired density.

Due to the decomposition of the H2O2, the mass is foamed within a few minutes and completely fills up the volume after approx. 10 minutes. The exothermic curing reaction starts after about 20 minutes, combined with a noticeable increase in the temperature of the mass, and is largely complete after about 60 minutes. The resulting foam has the following physical data:

Density: 300 kg / m ³

Thermal conductivity at 400 ° C: 0.2 W / m ^* K at 800 ° C: 0.35 W / m ^* K The inorganic foam is fine-pored, closed-celled as well as absolutely tight and resistant to all metal melts.

At a temperature of the molten metal 6 of 750 ° C, the temperature of the outer wall 3 is a maximum of 60 ° C.

4 shows the detail X according to an alternative embodiment of the invention in detail. Here, the inner wall made of refractory concrete is not, as shown in FIG. 3, additionally insulated with an insulating material 5 made of ceramic fibers, the thermal insulation 4 consists solely of the foamed mass. The thickness of the thermal insulation 4 is 350 mm in this embodiment.

In Figure 1 it is also shown that other parts of the furnace, such as the lid 9 for filling the liquid melt, the rear lid 10 for the removal of the liquid metal, the heated lid 11, the exhaust hood 12 and the soundproof hood 13 are also completely or partially consist of the foam used according to the invention.

Claims

Claims 1. Furnace (1) with an inner wall (2), an outer wall (3) and a heat insulation (4) arranged between the inner wall (2) and the outer wall (3), characterized in that the heat insulation (4th ) at least partially consists of an inorganic foam which is foamed and cured in situ from an inorganic curable composition, the composition being based on 100 parts by weight of a reactive solid (stone-forming component), 40 - 250 parts by weight of a water-containing hardener, which effects the hardening reaction of the reactive solid (stone-forming component) in the alkaline range, Contains 40 - 250 parts by weight of fillers and a blowing agent. 2. Furnace according to claim 1, characterized in that the inner wall (2) is covered at least in some areas of its surface with a second inorganic insulating insulating material (5), the elongation at break of which is higher than that of the cured inorganic foam. 3. Oven according to one of claims 1 or 2, characterized gekenn¬ characterized in that the cured inorganic foam is at least largely closed-cell design. 4. Oven according to one of claims 1 to 3, characterized in that the reactive solid (stone-forming component) one or more reactive solids from the group I fine-particle oxide mixture with contents of amorphous silicon dioxide and aluminum oxide, II glass-like, amorphous electrostatic filter ash, III ground calcined bauxite, IV electrostatic precipitator ash from lignite-fired power plants, V contains undissolved, amorphous SiO 2, in particular from an amorphous, disperse powder, dehydrated or water-containing silica or from high temperature processes (silica fume), VI Metakaoli. 5. Oven according to one of claims 1 to 4, characterized gekenn¬ characterized in that an alkali silicate solution with 1.2 to 2.5 moles of Si0 ₂ per mole of K ₂ 0 and / or Na2θ is used as the water-containing hardener. 6. Oven according to one of claims 1 to 5, characterized gekenn¬ characterized in that mainly mica and fine-grained talc are used as fillers in the foamable and curable inorganic mass. 7. Oven according to one of claims 1 to 6, characterized by a density of the inorganic foam of 120-350 kg / m ³ . 8. Oven according to one of claims 1 to 7, characterized gekenn¬ characterized in that the inorganic foam with the exception of openings in the walls in a completely closed area between the inner wall (2) and the outer wall (3) of the furnace (1) forms. 9. Oven according to one of claims 1 to 8, characterized gekenn¬ characterized in that the inorganic foam is impermeable to molten metal (6). 10. Oven according to one of claims 1 to 9, characterized gekenn¬ characterized in that hydrogen peroxide is used as a blowing agent. 11. A method for producing a furnace (1) with an inner wall (2), an outer wall (3) and a heat insulation (4) arranged between the inner wall (2) and the outer wall (3), characterized in that the intermediate - The space between the inner wall (2) and the outer wall (3) of the furnace (1) is filled with a foamable and curable mass to a part of its volume, the mass - to 100 parts by weight of a reactive solid ( stone-forming component), 40 - 250 parts by weight of a water-containing hardener, which effects the hardening reaction of the reactive solid (stone-forming component) in the alkaline range, Contains 40-250 parts by weight of fillers and a blowing agent, and that the mass is then foamed and cured in situ, so that the foam formed completely fills the space. 12. The method according to claim 11, characterized gekennzexchnet that mineral or ceramic fiber plates or • mats are applied to the inner wall (2) in at least a partial area of its surface before filling the foamable and curable mass. 13. Use of an inorganic foam which is foamed and cured in situ from an inorganic curable composition for the insulation of ovens, the composition being based on 100 parts by weight of a reactive solid (stone-forming component), 40 - 250 parts by weight of a water-containing hardener, which the hardening reaction of the reactive solid (stone-forming component) in the alkaline range, Contains 40 - 250 parts by weight of fillers and a blowing agent. 14. Use of an inorganic foam according to claim 13 as a front material in Al, Zn, GG, GS melting, Warm¬ holding and dosing furnaces. 15. Use of an inorganic foam according to claim 13 for coating furnace accessories such as hoods, covers, lids, channels, doors and chimneys, transport pans for liquid metal and preheating systems, against heat loss and as sound insulation.